A regenerative braking technology maximizes the fuel efficiency of a green vehicle, such as a hybrid vehicle, an electric vehicle, a fuel cell vehicle, and the like. The regenerative braking technology is a technology to generate electrical energy by applying a reverse torque to an electric motor and using the energy generated during braking. Thus, the electrical energy generated is stored in a high-voltage battery to be used later to power the motor. The regenerative braking technology is mostly applied to the green vehicles.
When vehicle braking is applied, a total braking amount is determined by a driver's braking request. In this case, regenerative braking takes charge of a portion of the total braking amount, and hydraulic braking other than regenerative braking is performed. Thus, if regenerative braking torque transmitted to wheels is accurately estimated, stable braking can be executed without any change in deceleration.
However, in a vehicle having a discrete variable transmission mounted therein, deceleration may vary due to the difficulty in precisely controlling regenerative braking when shifting gears during regenerative braking.
As shown in FIG. 1, in the conventional method, if a driver's braking intention is input (S10), a total braking amount is determined based on the driver's braking intention (S11). A regenerative braking allowance amount in the total braking amount is determined (S12), and it is then decided whether regenerative braking is possible (S13). In a case where regenerative braking is possible, the amount of regenerative braking is determined (S14), the amount of regenerative braking is compensated (S15), and a hydraulic braking amount is then determined (S16). In a case where regenerative braking is impossible, the hydraulic braking amount is immediately determined.
In this case, it is decided whether gear shifting is made through a transmission CAN signal. In a case where the gear shifting is made, the regenerative braking amount is calculated via an actual gear ratio. The regenerative braking amount is compensated to have a value approximate to the actual gear ratio based on a target gear step and a shifting phase.
However, in the conventional method, as shown in FIG. 2, there may occur a failure in compensating for the regenerative braking mount based on a braking degree and gear shifting. A sudden change in the hydraulic braking amount may be caused due to a sudden change in the regenerative braking amount. In addition, the linearity of braking may be deteriorated due to a sudden change in deceleration sensation.